EP 1 454 763 A2 discloses a method for finishing a wood or wood material board, in particular an MDF or HDF board, having an upper face and a lower face, in which, firstly, a sealing layer of melamine resin is applied to the upper face of the board, a decoration is printed onto the sealing layer and a protective layer of melamine resin is then applied to the decoration. The structure of the board is then pressed under the action of temperature until the protective layer and the sealing layer melt and are joined to each other with the inclusion of the printed decoration.
DE 195 32 819 A1 discloses a method for producing a wood material board having an optically configurable upper face, in which a base color, a seal, a printing base and a decorative print are applied successively to the wood material board. The printing base is built up from a base color or a base coat made of a paint seal and a surface paint. By means of engraved cylinders, a decorative print can be printed onto the printing base, for example in a two-color print. Finally, a multilayer acrylate UV paint, which can be cured by means of UV light, can be applied to this print.
DE 197 51 115 A1 discloses a method for coating a panel, in which at least one colored layer is applied to the upper face by means of a printing process, in particular by means of screen printing. The upper face can be untreated, polished or pre-treated, in particular painted. Finally, the colored layer applied can be covered by a coating with clear varnish.
If direct printing technology is used, that is to say the direct printing of the individual layers onto the substrate board, the result as compared with conventionally produced panels is a reduction in the thickness of the finished laminate panels as a result of the omission of the paper layers. This leads to problems during flow production when the large-format coated boards are subsequently divided up to produce the panels. In order that it is ensured that individual panels do not fall out of DIN 13329 as a result of an undersize of the thickness, a high level of quality assurance has to be provided, which firstly slows down production and secondly also increases the production costs. Ultimately, irritation also occurs at the dealer and/or end user, since the stack height of directly coated boards visibly differs from conventionally coated boards.
During the known board production, HDF boards are normally used as substrate boards, the upper face of which is ground off by about 0.3 mm. On the upper face and the lower face of the substrate board, a press skin is formed, which is also called press patina or decay layer. The press skin is produced as the fiber or chip cake is pressed and is produced by the hot upper face of the press platens or bands of the press. The press skin has a thickness of about 0.3 mm. Since the press skin is ground off completely and about 0.1 mm from the core material is ground off in order to reduce the roughness on the upper face of the substrate board before the further coating, the boards have to be produced thicker by a corresponding grinding allowance, which has a lasting influence on the production costs. In order to produce a flooring laminate meeting the standards, produced by means of direct printing technology and having a thickness of 6 mm, the substrate board must have a thickness of at least 6.1 mm.
The press skin therefore has to be ground off, since, in the area thereof, the input of heat during hot pressing is so high that the adhesive cures too quickly, as a result of which adhesive bonds at least partly break and make the applied layer susceptible. This breaking of the adhesive bonds makes finished panels susceptible to lifting of the decorative and wear-resistant layers applied to the substrate board. This lifting is called delamination, which can occur even under normal loading and from the change in size typical of wood materials on account of climatic fluctuations.
There is therefore a great need for wear-resistant laminate panels which lie within the thickness tolerance found in the above-mentioned standard. Furthermore, there is a need for a resource-preserving production method in which extra costs resulting from additional method steps and/or from additional materials are largely avoided.
In EP 2 236 313, which is not a prior publication, it is proposed to grind off only part of the press skin, specifically 0.1 mm thickness. As a result of this method, material savings of virtually 5% can be achieved, which means that wood, adhesive and some of the energy needed for the processing are saved. A 6 mm laminate panel meeting the standard can be produced by using the method described in this document from a substrate board which is 5.8 mm thick. In the case of a conventional production method, the substrate board must have a thickness of 6.1 mm.